How to Manage Pests

Pests in Gardens and Landscapes

Corn earworm (Tomato fruitworm)—Helicoverpa zea

The corn earworm or tomato fruitworm is a common caterpillar pest of many vegetables and flowers.  Newly hatched larvae have several rows of dark bristles on their backs.  Older larvae are striped but their body color varies from green or yellow to brown and is not reliable for identification. Many short, whiskerlike spines cover the body surface.

Identification of species | Life cycle

Damage

Earworms feed on leaves, buds, and flowers of many vegetable crops.  They destroy seedlings, bore into lettuce heads and bean pods, make deep watery cavities in fruit, and leave frass.  On corn, larvae eat through kernels of ears and feed on the developing tassels in the whorls of the plant. Damage is usually limited to the first 2 to 3 inches of the ear.

Solutions

On corn: Early planted corn is not as seriously affected as is late corn. Consider not treating, and simply cutting off damaged ends of corn at harvest. Applying a few drops of mineral oil with a medicine dropper to silks just inside each ear 3 to 5 days after silks first appear may be effective. Applications of insecticides, such as spinosad must be applied on silks within 3 days after first silks appear and at 3-day intervals until silks turn brown. Bacillus thuringiensis, a biological insecticide, may be dusted on silks every 3 days after 5 to 10% silk formation for partial control. Destroy culls and plants immediately after harvest.
On other vegetable crops and fruit:  Handpick.  Avoid spraying with insecticides. Bacillus thuringiensis, may kill 40 to 60% of the population but must be applied just after eggs hatch and before caterpillars enter fruit. Spinosad may also be effective. Plant early and harvest before late August. Disc or rototill plants immediately after harvest to reduce overwintering populations and prevent migration to neighboring crops.
Important natural enemies of the earworms include Hyposoter and Trichogramma parasites. General predators also feed on eggs and larvae.

Earworm larva feeding in tomato fruit
Earworm larva feeding in tomato fruit

Strawberr damage
Strawberry damage

Feeding on corn
Feeding on corn


Statewide IPM Program, Agriculture and Natural Resources, University of California
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